Process for producing cumene

ABSTRACT

A process for producing cumene is provided which comprises the step of contacting benzene and propylene under at least partial liquid phase alkylating conditions with a particulate molecular sieve alkylation catalyst, wherein the particles of said alkylation catalyst have a surface to volume ratio of about 80 to less than 200 inch −1 .

FIELD OF THE INVENTION

[0001] The present invention relates to a process for producing cumene.

BACKGROUND OF THE INVENTION

[0002] Cumene is a valuable commodity chemical which is usedindustrially for the production of phenol and acetone. Cumene has formany years been produced commercially by the alkylation of benzene withpropylene over a Friedel-Craft catalyst, particularly solid phosphoricacid or aluminum chloride. More recently, however, zeolite-basedcatalyst systems have been found to be more active and selective forpropylation of benzene to cumene. For example, U.S. Pat. No. 4,992,606describes the use of MCM-22 in the alkylation of benzene with propylene.

[0003] Typically, the zeolite catalysts employed in hydrocarbonconversion processes, such as aromatics alkylation, are in the form ofcylindrical extrudates. However, it is known from, for example, U.S.Pat. No. 3,966,644 that shaped catalyst particles having a high surfaceto volume ratio, such as those having a polylobal cross-section, canproduce improved results in processes which are diffusion limited, suchas the hydrogenation of resid.

[0004] Moreover, it is known from U.S. Pat. No. 4,441,990 that apolylobal catalyst particle having a non-cylindrical centrally locatedaperture can reduce the diffusion path for reagents and the pressuredrop across packed catalyst beds while minimizing catalyst loss due tobreakage, abrasion and crushing. In particular, Example 8 of the '990patent discloses that hollow trilobal and quadrilobal ZSM-5 catalystsare more active and selective for the ethylation of benzene at 770° F.and 300 psig pressure than solid cylindrical catalysts of the samelength. Under these conditions, the reagents are necessarily in thevapor phase.

[0005] Recently, attention has focused on liquid phase alkylationprocesses for producing alkylaromatic compounds, since liquid phaseprocesses operate at a lower temperature than their vapor phasecounterparts and hence tend to result in lower yields of by-products.Work by the present inventors has shown that shaped catalyst particles,such as those disclosed in U.S. Pat. Nos. 3,966,644 and 4,441,990 showlittle or no advantage when used in the liquid phase ethylation ofbenzene. Surprisingly, however, it has now been found that shapedcatalyst particles can yield improved results in the liquid phasepropylation of benzene to produce cumene.

SUMMARY OF THE INVENTION

[0006] In one aspect, the present invention resides in a process forproducing cumene which comprises the step of contacting benzene andpropylene under at least partial liquid phase alkylating conditions witha particulate molecular sieve alkylation catalyst, wherein the particlesof said alkylation catalyst have a surface to volume ratio of about 80to less than 200 inch⁻¹.

[0007] Preferably, the particles of said alkylation catalyst have asurface to volume ratio about 100 to about 150 inch⁻¹.

[0008] Preferably, the molecular sieve of the alkylation catalyst isselected from MCM-22, PSH-3, SSZ-25, MCM-36, MCM-49, MCM-56, faujasite,mordenite and zeolite beta.

[0009] Preferably, said alkylating conditions include a temperature ofabout 10° C. to about 125° C., a pressure of about 1 to about 30atmospheres, and a benzene weight hourly space velocity (WHSV) of about5 hr⁻¹ to about 50 hr⁻¹.

[0010] In a further aspect, the present invention relates to a processfor producing cumene which comprises the steps of:

[0011] i) contacting benzene and propylene with a particulate molecularsieve alkylation catalyst under at least partial liquid phase alkylatingconditions to provide a product containing cumene and apolyisopropylbenzene fraction;

[0012] ii) separating the polyisopropylbenzene fraction from theproduct; and

[0013] iii) contacting the polyisopropylbenzene fraction and benzenewith a particulate molecular sieve transalkylation catalyst under atleast partial liquid phase transalkylating conditions,

[0014] wherein the particles of at least said alkylation catalyst have asurface to volume ratio of about 80 to less than 200 inch⁻¹.

[0015] Preferably, the molecular sieve of the transalkylation catalystis selected from MCM-22, PSH-3, SSZ-25, MCM-36, MCM-49, MCM-56, ZSM-5,faujasite, mordenite and zeolite beta.

[0016] Preferably, said transalkylating conditions include a temperatureof about 100° C. to about 200° C.; a pressure of 20 to 30 barg, a weighthourly space velocity of 1 to 10 on total feed andbenzene/polyisopropylbenzene weight ratio 1:1 to 6:1.

DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention is directed to a process for producingcumene by reacting benzene with propylene under at least partial liquidphase conditions in the presence of a particulate molecular sievealkylation catalyst, wherein the particles of the alkylation catalysthave a surface to volume ratio of about 80 to less than 200 inch⁻¹,preferably, about 100 to about 150 inch⁻¹.

[0018] According to the invention, it has now been found that the liquidphase propylation of benzene, unlike the liquid phase ethylation ofbenzene, is sensitive to intraparticle (macroporous) diffusionlimitations. In particular, by selecting the shape and size of theparticles of the alkylation catalyst such that the surface to volumeratio is within the specified range, it is found that the intraparticlediffusion distance can be decreased without excessively increasing thepressure drop across the first catalyst bed. As a result, the activityof the catalyst for the propylation of benzene can be increased, whileat the same time the selectivity of the catalyst towards undesirablepolyalkylated species, such as diisopropylbenzene (DIPB) can be reduced.

[0019] Producing the alkylation catalyst with the desired surface tovolume ratio can readily be achieved by controlling the particle size ofthe catalyst or by using a shaped catalyst particle, such as the groovedcylindrical extrudate described in U.S. Pat. No. 4,328,130 or a hollowor solid polylobal extrudate as described in U.S. Pat. No. 4,441,990,the entire contents of both of which are incorporated herein byreference. For example, a cylindrical catalyst particle having adiameter of {fraction (1/32)} inch and a length of {fraction (3/32)}inch has a surface to volume ratio of 141, whereas a quadralobal solidextrudate having the external shape disclosed in FIG. 4 of U.S. Pat. No.4,441,990 and having a maximum cross-sectional dimension of {fraction(1/16)} inch and a length of {fraction (3/16)} inch has a surface tovolume ratio of 128. A hollow tubular extrudate having an externaldiameter of {fraction (1/10)} inch, an internal diameter of {fraction(1/30)} inch and a length of {fraction (3/10)} inch has a surface tovolume ratio of 136.

[0020] The alkylation catalyst used in the process of the inventioncomprises a crystalline molecular sieve selected from MCM-22 (describedin detail in U.S. Pat. No. 4,954,325), PSH-3 (described in detail inU.S. Pat. No. 4,439,409), SSZ-25 (described in detail in U.S. Pat. No.4,826,667), MCM-36 (described in detail in U.S. Pat. No. 5,250,277),MCM-49 (described in detail in U.S. Pat. No. 5,236,575), MCM-56(described in detail in U.S. Pat. No. 5,362,697), faujasite, mordenite,and zeolite beta (described in detail in U.S. Pat. No. 3,308,069). Themolecular sieve can be combined in conventional manner with an oxidebinder, such as alumina, such that the final alkylation catalystcontains between 2 and 80 wt % sieve.

[0021] The alkylation process of the invention is conducted underconditions such that both the benzene and propylene are under at leastpartial liquid phase conditions. Suitable conditions include atemperature of up to about 250° C., e.g., up to about 150° C., e.g.,from about 10° C. to about 125° C.; a pressure of about 250 atmospheresor less, e.g., from about 1 to about 30 atmospheres; a benzene topropylene ratio of about 1 to about 10 and a benzene weight hourly spacevelocity (WHSV) of from about 5 hr⁻¹ to about 250 hr⁻¹, preferably from5 hr⁻¹ to 50 hr⁻¹.

[0022] Although the alkylation process of the invention is particularlyselective towards the production of the desired monoalkylated species,cumene, the alkylation step will normally produce some polyalkylatedspecies. Thus the process preferably includes the further steps ofseparating the polyalkylated species from the alkylation effluent andreacting them with additional benzene in a transalkylation reactor overa suitable transalkylation catalyst. Preferably, the transalkylationreaction is conducted in a separate reactor from the alkylationreaction.

[0023] The transalkylation catalyst is preferably a molecular sievewhich is selective to the production of the desired monoalkylatedspecies and can, for example employ the same molecular sieve as thealkylation catalyst, such as MCM-22, PSH-3, SSZ-25, MCM-36, MCM-49,MCM-56 and zeolite beta. In addition, the transalkylation catalyst maybe ZSM-5, zeolite X, zeolite Y, and mordenite, such as TEA-mordenite.Preferably, the transalkylation catalyst is also arranged to have asurface to volume ratio of about 80 to less than 200 inch⁻¹, and morepreferably about 100 to about 150 inch⁻¹.

[0024] The transalkylation reaction of the invention is conducted in theliquid phase under suitable conditions such that the polyalkylatedaromatics react with the additional benzene to produce additionalcumene. Suitable transalkylation conditions include a temperature of 100to 200° C., a pressure of 20 to 30 barg, a weight hourly space velocityof 1 to 10 on total feed and benzene/PIPB weight ratio 1:1 to 6:1.

[0025] The alkylation and transalkylation steps of the process of theinvention can be conducted in an suitable reactor, such as a fixed ormoving bed or a catalytic distillation unit.

[0026] The following Examples will serve to further illustrate theprocess and some advantages of the present invention. In the Examples,catalyst performance is defined by reference to the kinetic rateconstant which is determined by assuming second order reaction kinetics.For a discussion of the determination of the kinetic rate constant,reference is directed to “Heterogeneous Reactions: Analysis, Examples,and Reactor Design, Vol. 2: Fluid-Fluid-Solid Reactions” by L. K.Doraiswamy and M. M. Sharma, John Wiley & Sons, New York (1994) and to“Chemical Reaction Engineering” by 0. Levenspiel, Wiley Eastern Limited,New Delhi (1972).

EXAMPLE 1

[0027] Benzene alkylation with propylene was conducted using aconventionally prepared MCM-49 catalyst. The catalyst was prepared byextruding a mixture of 80 wt % MCM-49 crystal and 20 wt % alumina intosolid cylindrical extrudates having a diameter of {fraction (1/16)} inchand a length of ¼ inch. The resultant catalyst particles had a surfaceto volume ratio of 72.

[0028] One gram of the catalyst was charged to an isothermal well-mixedParr autoclave reactor along with a mixture comprising of benzene (156g) and propylene (28 g). The reaction was carried out at 266° F. (130°C.) and 300 psig for 4 hours. A small sample of the product waswithdrawn at regular intervals and analyzed by gas chromatography. Thecatalyst performance was assessed by a kinetic activity rate constantbased on propylene conversion and cumene selectivity at 100% propyleneconversion. The results are described in Table 1.

EXAMPLE 2

[0029] The process of Example 1 was repeated with the catalyst beingproduced by extruding the mixture of 80 wt % MCM-49 crystal and 20 wt %alumina into solid quadralobal extrudates having a maximumcross-sectional dimension of {fraction (1/20)} inch and a length of ¼inch. The resultant catalyst particles had a surface to volume ratio of120.

[0030] When tested for the propylation of benzene under the conditionsused in Example 1, the catalyst of Example 2 gave the results shown inTable 1. TABLE 1 Catalyst Kinetic Rate Constant DLPB/Cumene (wt %)Example 1 185 14.6 Example 2 240 12.8

[0031] It will be seen from Table 1 that the shaped catalyst of Example2 exhibits higher activity and lower selectivity to undesirable DIPBthan the cylindrical catalyst of Example 1.

What we claim is:
 1. A process for producing cumene which comprises thestep of contacting benzene and propylene under at least partial liquidphase alkylating conditions with a particulate molecular sievealkylation catalyst, wherein the particles of said alkylation catalysthave a surface to volume ratio of about 80 to less than 200 inch⁻¹. 2.The process of claim 1 wherein the particles of said alkylation catalysthave a surface to volume ratio of about 100 to about 150 inch⁻¹.
 3. Theprocess of claim 1 wherein the molecular sieve of the alkylationcatalyst is selected from MCM-22, PSH-3, SSZ-25, MCM-36, MCM-49, MCM-56,faujasite, mordenite and zeolite beta.
 4. The process of claim 1 whereinsaid alkylating conditions include a temperature of about 10° C. toabout 125° C., a pressure of about 1 to about 30 atmospheres, and abenzene weight hourly space velocity (WHSV) of about 5 hr⁻¹ to about 50hr⁻¹.
 5. A process for producing cumene which comprises the steps of: i)contacting benzene and propylene with a particulate molecular sievealkylation catalyst under at least partial liquid phase alkylatingconditions to provide a product containing cumene and apolyisopropylbenzene fraction; ii) separating the polyisopropylbenzenefraction from the product; and iii) contacting the polyisopropylbenzenefraction and benzene with a particulate molecular sieve transalkylationcatalyst under at least partial liquid phase transalkylating conditions,wherein the particles of at least said alkylation catalyst have asurface to volume ratio of about 80 to less than 200 inch⁻¹.
 6. Theprocess of claim 5 wherein the particles of said alkylation catalysthave a surface to volume ratio of about 100 to about 150 inch⁻¹.
 7. Theprocess of claim 5 wherein the molecular sieve of the alkylationcatalyst is selected from MCM-22, PSH-3, SSZ-25, MCM-36, MCM-49, MCM-56,faujasite, mordenite and zeolite beta.
 8. The process of claim 5 whereinsaid alkylating conditions include a temperature of about 10° C. toabout 125° C., a pressure of about 1 to about 30 atmospheres, and abenzene weight hourly space velocity (WHSV) of about 5 hr⁻¹ to about 50hr⁻¹.
 9. The process of claim 5 wherein the particles of saidtransalkylation catalyst have a surface to volume ratio of about 80 toless than 200 inch⁻¹.
 10. The process of claim 5 wherein the molecularsieve of the transalkylation catalyst is selected from MCM-22, PSH-3,SSZ-25, MCM-36, MCM-49, MCM-56, ZSM-5, faujasite, mordenite and zeolitebeta.
 11. The process of claim 5 wherein said said transalkylatingconditions include a temperature of about 100° C. to about 200° C.; apressure of 20 to 30 barg, a weight hourly space velocity of 1 to 10 ontotal feed and benzene/polyisopropylbenzene weight ratio 1:1 to 6:1.